Cushioning device for hydraulic clutches



Feb. 26, 1952 2 SHEETS-SHEET 1 Filed Jan. 26, 1946 INVENTOR HENRYGRANDGIRARD ATTORNEYS Feb. 26, 1952 H. GRANDGIRARD 2,587,141

CUSHIONING DEVICE FOR HYDRAULIC CLUTCHES l Filed Jan. 26, 1946 2 SHEETS-SHEET 2 ,w W 7 2 3 9 .01 M M. W 6 A 1 2 s am" Patented Feb. 26, 1952UNITED STATES TENT OFFICE to Socit des' Brevets Kegresse, S. E. K.,Paris, France, al' corporation of France Application'January 26, 1946,Selial'No.v 643,806j In France. December 22, 1943 Sectonl', Publi'cLaw690, August' 8, 1946 Patent expires Decemberv 22, 1963 1 Claim.

The present invention relates to' hydraulicallyy actuated clutches ofthe type in whichthe discs are: hydraulically compressed by means of annular plates or pistons. In such clutches. arr

undesirable slipping is observed as soon as. the. flow of pressure.fluid ceases. This phenomenon. is.` due to the incompressibility of' theactuating fluid, combined with the inevitablelack of fluid'- tightnessof the joints inthe circulation system ofthe fluid' and mainly betweenthe rotating and fixed parts of the clutch. In these conditions, the'pressureA of the iiuid` drops immediately when the supply ceases.

This slipping is harmful in all clutches; it is in particularincompatible with the satisfactory operation of the change speedgearsof: automobile transmissions having. two.. clutches which arehydraulically controlled' andl alternatively ensure the changing of thesuccessive gears, In such transmissions, it is, infact, indispensablefor theclutch controlling the' operative gear t'o continue to transmitthe powerl of the: engine after the flow of. the pressureruid hasceasedin said clutch, atleast. during thel time necessary for-theengagement of the next -g'ear andi for. the setting in operation of theother clutch; if it were otherwise, a gap would occur in the drive ofthe vehicle.

The present invention has for an object a clutch arrangement whichenables the losses of fluid in one clutch to be temporarily compensatedfrom the instant when the flow of the fluid ceases, and thereby tomaintain a suicient pressure behind the actuating piston of that clutchto permit the discs to remain compressed during the time necessary forthe engagement of the other clutch corresponding to the adjacent gear.

According to -the invention, resilient members are interposed betweenthe piston and the pressure plate, said members serving during theirextension from a compressed condition temporarily to compensate forleakage in the fluid system, thereby stabilizing at a minimum value thebearing pressure of the clutch plate. These resilient members serve toextend the period during which the clutch plates are in drivingengagement.

The resilience of said members is preferably such that when they areextended, they correspond to the minimum bearing pressure necessary toproduce the drive and, when they are compressed, they correspond to themaximum bearing pressure provided for between the clutch plates.

The accompanying drawings show, by Way of 2 example, one embodimentl ofthe invention. In` said drawings:

Figure 1 is a half elevation of the gen'erlallarIV-` rangement oftheimproved clutch according' to'A the invention (the cover' and the pistonbeing removed in the right-handv portion of this iig'- ure);

Figure 2 is a section on line A-B of Figure'l.;

Figure 3V shows, on a larger scale, one of the resilientmembers providedaccording to tl'ief invention';

Figure 4'- isa section similar t'o'li'gure 2,`show ing the positions of:the annular piston and pressure plate with the clutch disengaged;

Figure' 5 is a similarse'cti'on showing the posi`= tions of the annularpiston and pressure' platel with the clutch fullyengaged byf the actionofV the actuatinguid'; and

Figure 6 is another similar section showingy thel position ofitheannularpiston and pressure plate during extended engagement of thev clutch whenthe flow of thelactuatin'gfluid ceases'and its pres"- sure is reduced byleakage.

Referring tothe drawings,v l designates'the'flywheel, which mayconstitute theV fixed plate'- of the clutch, 2 the clutch disc, 3 themovable pressure plate, 4 the annular actuating piston, 5 the cover ofthe clutch carrying the ducts and distribution members (not shown) forthe fluid, and 6 the retracting springs of the pressure plate.

These various elements and their operation are known. The improvementsin this arrangement, according to the invention, consist in interposingbetween the plate 3 and the piston 4 a number of resilient memberscomprising, for example, pushers such as that illustrated in Figure 3, asuflcient number of which pushers being provided to produce the pressurenecessary for the engagement of the clutch and being located in housingswhich are uniformly distributed over the opposed faces of the plate andpiston.

Each resilient member comprises, in the embodiment shown, a spring Il, acup 1, to which is secured a stem 8, and a second cup 9 movable on thestem in the direction of compression of the spring but which, in theopposite direction, abuts against a head I0 on the stem 8, thereby tokeep the spring under va predetermined tens1on.

The strength and flexibility of the springs according to the inventionare so calculated that rstly, when all the resilient members are freewith the cups 9 abutting against the heads I0, their total forcecorresponds to the vminimum pressure which has to be exerted on the disc2 to keep the clutch engaged, and to transmit the maximum power withoutslipping; and, secondly they are completely compressed when the maximumpressure of the actuating fluid is eX- erted behind the piston 4,thereby enabling said piston to come into direct contact with the plate3. In practice, the values of these two extreme pressures are in theratio of 3 to 4 in the present embodiment. r

The mechanism of this invention operates in the following manner,reference being made to Figures 4, 5 and 6:

During disengagement of the clutch, no pressure iiuid is supplied behindthe piston 4. The springs 6 push back the plate 3 and the piston 4,thereby releasing the disc 2, which moves away from the flywheel I, asshown in Figure 4.

With total engagement of the clutch, as shown in Figure 5, the disc 2 iscompressed by the action of the pressure fluid supplied behind thepiston 4 and the latter, after having compressed the springs Il, comesdirectly into contact with the plate 3. The plate-piston unit thus movestowards the iiywheel l, and presses the clutchA disc 2 thereagainst. Atthis phase of the operation, the action ofthe resilient members providedaccording to the invention is therefore eliminated.

If the supply of fluid ceases and leakages have allowed the escape of apart of thevliquid, so that the pressure drops, though notto zero, thesprings Il, in expanding, enable the piston 4 to move backwardlyrelatively to the plate 3, thereby compensating for the volume of liquidlost; the pressure exerted by the clutch disc 2 therefore stillcorresponds, during this period, to the force necessary for transmittingthe power of the engine, since the strength and the number of thesprings Il have been chosen precisely for this purpose. This state ofequilibrium, illustrated in Figure, remains prevalent until the instantwhen the cups 9 abut against the heads I0.

The time during which this stabilization of the pressure is eiectivedepends, of course, on the extent of the leakage in the circulationsystem of the uid, on the viscosity of the fluid, and also on the extentof travel which is permitted for the cup 9; in practice it is suicient,however, in a, change speed gear such as that above mentioned, to permitthe lling of the second clutch.

While the drawings show only one embodiment of the invention, numerousconstructional modifications can be made within the scope of theappended claim.

What I claim is:

In a hydraulically controlled clutch comprising a driving membercontrolled by an annular piston rotatable therewith and displaceable byfiuid pressure, the uid acting in an annular pressure chamberaccommodating the piston, a plurality of resilient members interposedbetween the driving member and piston, each resilient member comprisinga pair of cups, a coil spring compressed between said cups, and a, stemcoaxially arranged with respect to said cups and spring and fixed to oneof said cups, said other cup being slidable on said stem, said stembeing provided with an abutment arresting said slidable cup at apredetermined extension value of said spring, said annular piston havingvtransverse extensions directed toward the driving member and cominginto direct contact therewith when the springs are completelycompressed.

HENRI GRANDGIRARD.

REFERENCES CITED The following references are of record in the iile ofthis patent:

UNITED STATES PATENTS Number Name Date 786,294 Joy Apr. 4, 19051,442,092 Parsons et al Jan. 16, 1923 1,648,864 Pugh Nov. 8, 19271,913,525 Valentine et al. June 13, 1933 2,123,867 Criley July 19, 19382,386,220 Lawler et al. Oct. 9, 1945

